Sources of error for abnormal monocular fixation and tracking movements will be examined for amblyopic eyes. Parameters resulting in abnormal vergence eye movements will be identified for non-paralytic strabismus. Abnormal sensory aspects of binocular vision, including suppression and reduced stereopsis will be quantified in non-paralytic strabismus. Possible relationships will be examined between abnormal sensory and motor aspects of binocular vision in individuals with strabismus. Results will clarify the factors which contribute to reduced visual acuity in amblyopia and abnormal fusional vergence in strabismus. This information will lead to a refinement in diagnostic procedures and will also provide a sensitive means for evaluating the effectiveness of various therapeutic procedures.